The receiver associated with this ST-BICM emission scheme, proposed by Tonello in the above-mentioned article, is iterative, as illustrated in FIG. 2. It is fed with signals received on each of the NR receiving antennas referenced 251, 252 to 25NR, and comprises a first space-time “MIMO demapping” module 23 (MIMO M−1) using an ML (maximum likelihood) type algorithm analyzing especially the log likelihood ratio (LLR) on each encoded bit. A “demapping” module M−123 such as this performs an operation that is appreciably the reverse of that of the “mapping” module M 13 and has Nt outputs, where Nt is the number of emission antennas that supply a parallel/series conversion P/S module 241, then a de-interleaving module 221.
The log likelihood ratios derived from the MIMO demapping module M−1 23 are then improved via a SOVA (Soft Output Viterbi Algorithm) type channel decoder CC−1 21 and again sent to the “MIMO demapping” module M−1 23, after a new interleaving II 222, and a new series/parallel conversion S/P 242. This process is reiterated in order to improve the decoded data.
In this reception technique, it is therefore sought by maximum likelihood to find out which symbol of the constellation has been emitted on each of the antennas. The use of such a receiver requires a preliminary initializing phase during which each of the transmission channels between the Nt emission antennas and the NR receiving antennas is estimated in emitting symbols of which the receiver has a priori knowledge.
One drawback of this prior art iterative technique is its complexity of implementation owing to the use of a maximum likelihood type of algorithm at reception. Such an algorithm entails exhaustive computation of all the sequences of received symbols possible and a selection, from among these sequences, of the most likely one. The complexity of such an algorithm increases exponentially as a function of the number of emission antennas, the number of receiving antennas and the size of the constellation used (or again the number of states of the modulation).